1. Field of the Invention
The present invention relates to couplings for joining tubes that carry fluid and more particularly to the field of quick-connect couplings of this type.
2. Description of the Prior Art
The tubular coupling described in U.S. Pat. No. 4,055,359 permits a fluid-tight connection to be made between the tubes by hand in a short time. In making this connection the operator applies axial force to one of the tubes and a resistant force in the opposite direction to the other tube. This action causes a garter spring to expand around the flared end of one of the tubes and into a locking position within a cage member. It is necessary in joints of this type that carry pressurized fluid that a positive hydraulic seal be an integral part of the joint. The coupling described in the patent includes at least one O-ring received in a groove formed in one tube. The O-ring is compressed when the second tube is inserted over the first tube with an interference fit between the O-ring and a second tube.
One problem with this coupling arises because of the frictional contact between the O-rings and the metal tube end. The O-rings are compressed in order to produce the required seal but this compression produces a frictional force between the O-rings and the second tube. The magnitude of the force is sufficient to hold the tube ends together even though the garter spring has not been expanded over the flared end of the second tube and into its locking position. Often in the assembly process it has been discovered that the coupling gives the appearance of a properly connected coupling because the frictional forces hold the tube ends in substantially the same relative positions they would have if the connection were properly made. If the garter spring has not been forced to its locking position the tube ends retained only by the friction force are readily separated when the fluid circuit is pressurized under operating conditions. Loss of the fluid carried in the system requires its replacement and time is required to locate the source of the leak and to properly connect the coupling.
A threadless coupling for joining two tubes would preferably apply a force during assembly to the tube ends tending to overcome the frictional force that develops between the O-rings and the second tube that compresses them. Furthermore, a joint of this type would preferably provide means for readily observing the latching members of the coupling to assure that they are properly located and that a positive connection is made.